Ugh, stop talking about Congo, you guys.
I saw this last night and was really impressed. I agree with the Lean/Huston, "old-fashioned" feel others have pointed out. It reminded me very much more of movies before the year 2000 than movies since then. In addition to the likes of The Bridge over the River Kwai, Lawrence of Arabia, Herzog's "jungle movies" (though obviously more mainstream), The African Queen, and The Treasure of the Sierra Madre, the other movie that immediately came to mind was The Ghost and the Darkness. Old-fashioned but at the same time feeling free to depart from Hollywood conventions (or at least contemporary, post-2000 ones). Not afraid to go for some stylistic flourishes (like the jump-cut from Robert Pattinson's booze getting poured down the drain to the train speeding through the countryside), but never letting the style overwhelm the substance.
The word that kept coming to my mind about the filmmaking was "confidence." This is a movie that knows what it wants to do and how to go about doing that. I was curious the whole time what else James Gray had done, and looking up his filmography after the movie I didn't expect the movies I saw there. The only previous movie of his I've seen is Two Lovers, which is beautiful and touching in a lot of ways but centers around a downright baffling performance by Joaquin Phoenix (two beautiful women fall in love with him, but he basically acts like a mumbly 14-year-old boy the whole time). Between that, some crime thrillers starring Phoenix and Mark Wahlberg, and The Immigrant (which I haven't seen), I wouldn't have expected The Lost City of Z to be the next installment in his body of work. Color me pleasantly surprised.
Also, I was delighted by the opera they found during their first expedition. "Oh, they just stumbled into Fitzcarraldo! Neat!"